There are existing communication devices that utilize a single high-frequency front-end module that processes communication signals of two adjacent frequencies. For example, there is a high-frequency front end that transmits/receives a Wifi signal and a BlueTooth signal, both of which use the 2400 MHz band, at the same time.
In such a high-frequency front-end module, coupling between two antennas for transmitting/receiving respective two communication signals of adjacent frequencies becomes a problem. In particular, in a high-frequency front-end module included in a small-sized communication apparatus, it is difficult to set a long distance between two antennas and mutual interference becomes a more serious problem.
An antenna module disclosed in Patent Document 1 (identified below) includes a monopole antenna and a loop antenna. The loop antenna is a half-ring-shaped λ/2 loop antenna, and an end portion of the loop antenna adjacent to the monopole antenna is connected to the ground. With this configuration, a current flowing to the ground is reduced and the isolation between the monopole antenna and the loop antenna is ensured.
Patent Document 1: Japanese Patent No. 4297012.
However, there are frequency bands in which sufficient isolation cannot be ensured with the configuration disclosed in Patent Document 1. For example, in the 2400 MHz band, the isolation of only 10 dB is ensured with the configuration disclosed in Patent Document 1.